diff --git a/Sources/Defaults/Defaults.swift b/Sources/Defaults/Defaults.swift
index e6f807f..09b94b8 100644
--- a/Sources/Defaults/Defaults.swift
+++ b/Sources/Defaults/Defaults.swift
@@ -49,7 +49,13 @@ extension Defaults {
 		public let name: String
 		public let suite: UserDefaults
 
+		@_alwaysEmitIntoClient
 		fileprivate init(name: String, suite: UserDefaults) {
+			runtimeWarn(
+				isValidKeyPath(name: name),
+				"The key name must be ASCII, not start with @, and cannot contain a dot (.)."
+			)
+
 			self.name = name
 			self.suite = suite
 		}
@@ -88,7 +94,8 @@ extension Defaults {
 		- `UserDefaults.object(forKey: string)` returns `nil`
 		- A `bridge` cannot deserialize `Value` from `UserDefaults`
 		*/
-		private let defaultValueGetter: () -> Value
+		@usableFromInline
+		internal let defaultValueGetter: () -> Value
 
 		public var defaultValue: Value { defaultValueGetter() }
 
@@ -99,6 +106,7 @@ extension Defaults {
 
 		The `default` parameter should not be used if the `Value` type is an optional.
 		*/
+		@_alwaysEmitIntoClient
 		public init(
 			_ key: String,
 			default defaultValue: Value,
@@ -135,6 +143,7 @@ extension Defaults {
 
 		- Note: This initializer will not set the default value in the actual `UserDefaults`. This should not matter much though. It's only really useful if you use legacy KVO bindings.
 		*/
+		@_alwaysEmitIntoClient
 		public init(
 			_ key: String,
 			suite: UserDefaults = .standard,
@@ -144,18 +153,22 @@ extension Defaults {
 
 			super.init(name: key, suite: suite)
 		}
+	}
+}
 
-		/**
-		Create a key with an optional value.
+extension Defaults.Key {
+	// We cannot declare this convenience initializer in class directly because of "@_transparent' attribute is not supported on declarations within classes".
+	/**
+	Create a key with an optional value.
 
-		- Parameter key: The key must be ASCII, not start with `@`, and cannot contain a dot (`.`).
-		*/
-		public convenience init<T>(
-			_ key: String,
-			suite: UserDefaults = .standard
-		) where Value == T? {
-			self.init(key, default: nil, suite: suite)
-		}
+	- Parameter key: The key must be ASCII, not start with `@`, and cannot contain a dot (`.`).
+	*/
+	@_transparent
+	public convenience init<T>(
+		_ key: String,
+		suite: UserDefaults = .standard
+	) where Value == T? {
+		self.init(key, default: nil, suite: suite)
 	}
 }
 
diff --git a/Sources/Defaults/Utilities.swift b/Sources/Defaults/Utilities.swift
index 6d6c86d..ecdf4ea 100644
--- a/Sources/Defaults/Utilities.swift
+++ b/Sources/Defaults/Utilities.swift
@@ -1,5 +1,9 @@
 import Foundation
-
+#if DEBUG
+#if canImport(OSLog)
+import OSLog
+#endif
+#endif
 
 extension Decodable {
 	init?(jsonData: Data) {
@@ -160,6 +164,13 @@ extension Collection {
 	}
 }
 
+extension Defaults {
+	@usableFromInline
+	internal static func isValidKeyPath(name: String) -> Bool {
+		// The key must be ASCII, not start with @, and cannot contain a dot.
+		return !name.starts(with: "@") && name.allSatisfy { $0 != "." && $0.isASCII }
+	}
+}
 
 extension Defaults.Serializable {
 	/**
@@ -200,7 +211,8 @@ extension Defaults.Serializable {
 	set(Value.toSerialize(value), forKey: key)
 	```
 	*/
-	static func toSerializable<T: Defaults.Serializable>(_ value: T) -> Any? {
+	@usableFromInline
+	internal static func toSerializable<T: Defaults.Serializable>(_ value: T) -> Any? {
 		if T.isNativelySupportedType {
 			return value
 		}
@@ -217,3 +229,54 @@ extension Defaults.Serializable {
 		return toSerializable(next)
 	}
 }
+
+#if DEBUG
+/**
+Get SwiftUI dynamic shared object.
+
+Reference: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/dyld.3.html
+*/
+@usableFromInline
+internal let dynamicSharedObject: UnsafeMutableRawPointer = {
+	let imageCount = _dyld_image_count()
+	for imageIndex in 0..<imageCount {
+		guard
+			let name = _dyld_get_image_name(imageIndex),
+			// Use `/SwiftUI` instead of `SwiftUI` to prevent any library named `XXSwiftUI`.
+			String(cString: name).hasSuffix("/SwiftUI"),
+			let header = _dyld_get_image_header(imageIndex)
+		else {
+			continue
+		}
+
+		return UnsafeMutableRawPointer(mutating: header)
+	}
+
+	return UnsafeMutableRawPointer(mutating: #dsohandle)
+}()
+#endif
+
+@_transparent
+@usableFromInline
+internal func runtimeWarn(
+	_ condition: @autoclosure() -> Bool, _ message: @autoclosure () -> String
+) {
+#if DEBUG
+#if canImport(OSLog)
+	let message = message()
+	let condition = condition()
+	if !condition {
+		os_log(
+			.fault,
+			// A token that identifies the containing executable or dylib image.
+			dso: dynamicSharedObject,
+			log: OSLog(subsystem: "com.apple.runtime-issues", category: "Defaults"),
+			"%@",
+			message
+		)
+	}
+#else
+	assert(condition, message)
+#endif
+#endif
+}
diff --git a/Tests/DefaultsTests/DefaultsTests.swift b/Tests/DefaultsTests/DefaultsTests.swift
index 49c4d41..3dbfc99 100644
--- a/Tests/DefaultsTests/DefaultsTests.swift
+++ b/Tests/DefaultsTests/DefaultsTests.swift
@@ -1,7 +1,7 @@
 import Foundation
 import Combine
 import XCTest
-import Defaults
+@testable import Defaults
 
 let fixtureURL = URL(string: "https://sindresorhus.com")!
 let fixtureFileURL = URL(string: "file://~/icon.png")!
@@ -37,6 +37,15 @@ final class DefaultsTests: XCTestCase {
 		XCTAssertTrue(Defaults[key])
 	}
 
+	func testValidKeyName() {
+		let validKey = Defaults.Key<Bool>("test", default: false)
+		let containsDotKey = Defaults.Key<Bool>("test.a", default: false)
+		let startsWithAtKey = Defaults.Key<Bool>("@test", default: false)
+		XCTAssertTrue(Defaults.isValidKeyPath(name: validKey.name))
+		XCTAssertFalse(Defaults.isValidKeyPath(name: containsDotKey.name))
+		XCTAssertFalse(Defaults.isValidKeyPath(name: startsWithAtKey.name))
+	}
+
 	func testOptionalKey() {
 		let key = Defaults.Key<Bool?>("independentOptionalKey")
 		let url = Defaults.Key<URL?>("independentOptionalURLKey")